Rheostat and the like



2 Sheets-Sheet l 17a/@Www N. C. SCHELLENGER RHEOSTAT AND THE LIKE Filed oct. 26; 1931 Feb. 13, 1934.

Feb. 13, 1934; N, -c. scHELLENGER 1,947,437

HHEOSTAT AND THE LIKE Filed oct. 26,19% 2 sheets-sheet 2 (bf/fg@ Patented Feb. 13, 1934 UNITED STATES PATENT OFFICE anEosrAr AND THE Lum f Application October 26, 1931. Serial No. 571,101

c claims. (Cl. aol-55) This invention relates to a process of making rheostats and the like.

It is oldv in the prior art to provide rheostats consisting of a cup-like metallic frame which is lined by a suitable insulation, and contains a resistance strip disposed inside of the shell and against the insulation lining. The present invention relates to the manufacture of a rheostat of this kind, and refers more particularly to an improved process for securely xing the resistor strip in place in the shell.

Insulating materials such as ber, certain phenol condensation products, and the like, are somewhat hygroscopic, and will absorb a certain amount of moisture. The materials expand as moisture is absorbed and contract as it is exfpelled. My improved process makes use of this property of insulating'material to rigidly bind the resistance strip and insulating lining in the metallic shell of a rheostat.

In the preferred embodiment of my invention, sheets of insulation of suitable thickness and character for the purpose desired are thoroughly dehydrated in any convenient manner and while dehydrated are blanked into strips of shape and size determined by the device being manufactured. After the blanking is completed these strips are stored under such conditions that there is no likelihood of their absorbing moisture. The insulating strip upon which the resistance unit is to be wound is taken from this storage device .and the wire is wound upon it under conditions which insure that the absorption of moisture will r be negligible. If necessary after the winding operation is completed the units are returned to a suitable storage device where they remain until needed under conditions which prevent the absorption of the moisture by them.

The lining insulators with which the metallic shell or frame of the device is lined are similarly blanked from dehydrated insulation and stored in such a manner that they will not absorb moisture.

Upon assembly of the unit, the insulating lining is rst placed within the shell with its ends overlapping, and then expanded mechanically to bring its ends in alignment and abutting each other. The terminals and other auxiliary devices are placed in the shell against this insulation and the resistance strip then placed inside of such devices. The ends of the resistance strip are overlapped and it is expanded mechanically to bring those ends into alignment and to abut them against each other. This compresses the stripv under considerable pressure against its own hoop strength, and it is held by the tension in the me- 'tallic shell itself.

The process is completed by first 'allowing the insulation of the rheostat to absorb a certain amount of water, which causes the insulators to expand and more rmly bind themselves in the metallic shell. After the required amount of water has been absorbed the moisture Pcontent of the strip is maintained constant by a sealing these properties may be utilized to securely bind the elements in the frame of a rheostat or other similar device.

My invention will best be understood by reference to the accompanying drawings in which sumcient details oi' the construction of a rheostat are shown to permit `a. clear understanding of the invention, and in which:

Figure 1 is a diagram illustrating the manner of blanking the insulators from a sheet o! dehydrated insulation;

Figure 1a is a similar view illustrating the blanking of the winding strip from a sheet oi' dehydrated material;

Figure 2 is a plan view of one oi' the insulators so prepared;

Figure 3 is a similar view of a companion insulator;

Figure 4 is a plan view oi the resistor unit after it has been wound;

Figure 5 is a similar view of the resistor unit after it has been trimmed preparatory to insertion in the frame or shell of the rheostat;

Figure 6 is a perspective view of a shell with the insulator lining in place in it; 1 i

Figure 'I is a cross sectional view of a partially assembled rheostat with the expanding device in place in it;

Figure 8 is a view similar to Figure '1 with the expanding device inits operated position;

Figure 9 is a plan view of the rheostat at the end of the next step in the process of assembly;

Figure 10 is a cross sectional view taken substantially along the line 1010 o1' Figure 9 showing the rheostat with the expanding member in place in it;

Figure 11 is a view similar to Figure 10 after the expanding member has been operated and removed and diagrammatically illustrating a succeeding step in the process;

Figure 12 is a fragmentary cross sectional view similar to Figure 11 and diagrammatically illustrating another step in the process of my invention;

Figure 13 is a plan view of a completely assembled unit made in accordance with theteachings of my invention; and

Figure 14 is a plan view of a modified form of shell which may be used Within the process of my invention.

Referring now to the drawings in more detail, a sheet of suitable insulation 1 is thoroughly dehydrated to bring its moisture content down to a very low figure. This insulation may be fiber,

or a phenol condensation product composed of :ber insulating material bonded together with a phenol condensation binder commonly known as bakelite. In any event, the insulating material is brous in nature and will expand somewhat upon absorbing moisture and contract as the moisture is expelled from it. The dehydration of the insulating sheet 1 lmay be carried on in any preferred manner such as by heat or vacuum treatment, or a combination of these two treatments.

Certain insulating materials of this kind are known to expand more in one direction with respect to their grain thanin the opposite direction when they are permitted to absorb moisture, and if the sheet of insulation 1 is of this nature it is carefully noted in which direction maximum expansion will occur, so that the insulating devices blanked out of it will be formed with their longitudinal `axes lying in the direction of maxi-J In Figure 1 I have illustrated by the arrows 2 the direction in which the maximum expansion will occur when the sheet 1 is permitted to absorb moisture. Insulators 3 and 4 are shown in dotted lines, these insulators being blanked out of the sheet 1 by a suitable punchpress operation. The particular shape and size of the members 3 and 4 is obviously shown by way of example as this will' be determined by the particular requirements of the device being manufactured.

In Figures 2 and 3 I have shown insulators 3 and 4 blanked from a sheet such as the sheet 1. 'I'hese particular insulators will be recognized as the lining members employed in the formation of a tandem type rheostat such as is shown in my copending application Serial No. 518,281, filed February 25, 1931. The insulator 3 contains projecting bosses 6 registering with depressions 7 in the insulator 4 to position the two halves of the tandem rheostat in definite relation with respect to each other. Insulators 3 and 4 also contain circular openings 8 and slit-like openings 9 for purposes which will hereinafter appear.

After the members 3 and 4 have been blanked they are stored under such conditions that there is no likelihood of their absorbing moisture. Since the members 3 and 4 are highly dehydrated they are inclined to be somewhat brittle and must be carefully handled to prevent them from breaking and also tojprevent them from absorbing of moisture before it is desired that they should. I have found that a temperature controlled oven is a convenient storage receptacle for these mem- ,bers after they have lbeen blanked and before they are needed for assembly in a unit. By naintaining the temperature of the oven high and its moisture content low, the amount of moisture 'that is absorbed by the members 3 and 4 while they are in it can be kept negligible.

In Figure la, I have illustrated the manner of blanking the strip 5 from a sheet of dehydrated insulation 1', the direction of maximum expansion being indicated by the arrow 2. Preferably this sheet 1 is composed of a fibrous phenol condensation product which is somewhat thicker than theA sheet 1 from which the insulators 3 and 4'are blanked. The size and shape of sheets 1 and 1' are Ashown by Way of example only.

Certain materials such as fiber, become brittle when dehydrated and under such circumstances I contemplate partially dehydrating the sheet prior to blanking and then further dehydrating the forms blanked from it. I have found that materials of this kind can be successfully worked without excessive breakage when their moisture content is about 50% normal, and that the forms blanked from such a sheet can be assembled when their moisture content is still further reduced, say to about 10% normal. These figures will of course vary with' the material used, and I am not to be limited by them. Certain other materials can be completely dehydrated without rendering them too brittle to handle.

The strips 5 similarly blanked from the dehydrated sheet 1' are wound with a wire resistance Winding 10 which may be composed of two sections 11 and 12 joined together by a suitable coupling means 13. The exact details of this winding will of course vary to meet the requirements of the-particular unit being fabricated. -Care is taken during the winding operation so that the amount of moisture absorbed by the insulator 5 is kept down to a After the units have been blanked and before they are wound, and after they have been wound and before they are needed in assembly, they are preferably stored'in a receptacle suitably adapted to prevent any great amount of change in their moisture content.

After these insulators have been blanked and wound in the foregoing manner, they are ready for assembly into the unit being manufactured. For example, if the unit is a rheostat it may conveniently comprise a cylindrical metallic shell 15 having closed end 16 and side Walls 17 disposed as a flange projecting from the closed end 16. A suitable disc of insulating material 18 is first disposed within the shell at the junction of its closed end 16 and walls 17, and an insulator such as 3 is disposed around the inside surface of the flange section of the wall 17 and against the disc 18, as shown in Figures 6, 7 and 8. It will be noted that the length of the insulator 3 is greater than the perimeter of the inside surface of the wall 17 of the shell and that the ends of the insulator therefore overlap as at 19. The amount of this overlap may be varied and will of course depend upon the thickness of the stock from which the insulator 3 is blanked.

The next step in the process consists in ex- Dandng -the insulator 3 to position it firmly against the inside surface of the wall 17 of the shell and with its ends abutting. This operation may be performed in a number of `ways, for example, a cylinder 20 composed of resilient material such as live rubber may be placed in the shell r15 where it loosely fits within the insulator 3. The cylinder 20 is sufficiently long that it projects well above the free edge of the wall longitudinally of its axis, the closed end 16 of.

the shell being suitably supported upon a table 22 of the press during this operation.

` Compression of the cylinder 20 along its 1ongitudinal axis will'expand it radially and thus cause it to force the insulator 3 tightly against`Y` the wall 17 of the shell. If necessary, suiiicient pressure may be exerted by the plunger 21 to cause the cylinder 20 to expand suiiiciently to force the wall 17 of the shell outward slightly. 'Ihis will obviously increase the perimeter of the inside surface of the wall 17 and the ends of the insulator 3 will be aligned in abutting relation as shown at 23 in Figure 8. When the pressure is removed from the block 20,'that block willspring back into its normal Shape, and the insulator 3 will beheld in the shell by .its-own hoop strength in compression.

As will be seen in Figure 6, the shell 15 contains generally rectangular openings 24 in its Wa11`17, and the insulator 3 is positioned in the shell in such a manner that the lslots 9 in it registerv with these rectangular slots in the shell. The next step in the operation of assembling the units consists in pushing terminals such as 27 through the slot 9 in the insulation and through the slot 24 in the shell preparatory to receive the resistor unit 10. This unit is then removed from its storage place and trimmed so that its length corresponds accurately` to the inside perimeter of the lined shell. As will be seen in Figure 4,/the unit is blanked somewhat longer than isrequired and contains oval shaped indentations 25 in its opposite end. After the unit has been trimmed accurately to length these indentations are semi-circular as shown at 26 in Figure 5, and jare employed for a purpose which will hereinafter appear. The unit is immediately placedinside of the shell against theinsulator 3 and upon the disc 18 located therein, with its ends overlapping as shown at 28 in Figure 9. The overlapping ends are located midway between the slot 24 in the shell as shown.

A resilient block 29, similar to the block 20, is next insertedinside of the unit and compressed, as shown, to expand the unit 10 radially outward against the insulator 37. This expansion may also be sufficient to expand the wall 17 of the shell, and is continued until the overlapped ends 28 ofthe unit 10` are aligned in abutting relation'to' each other as shown at 30 in Figure 1l. It will be noted that the two semi-circular indentations 26r now register to form a generally circular opening in the strip l0, which is, aligned with a circular` opening 3l in the shell, for a purpose which will hereinafter appear. Y

After the block 29l has been sumciently com-f pressed to expand the resistance strip 10 into the desiredposition, pressure on it is removed and it is allowed to contract back into the shape shown in` Figure 10, and it is then removed from the unit. The resistor strip 10 is now held in I Place in the shell by its 'own hoop strength in compression. v

'Ihe next step in the process of manufacture I of a unit consists in hydrating thelnsulators 3 and 10. In Figure 11 I have ditically illustrated a method of doing this, which consists of spraying the insulation by finely divided spray forced out of the nozzle 32 of a suitable pressure gun. This sprayA is preferably composed of chemically pure water, and the insulators 10 and 3 are quite thoroughly wetted by it. Obviously this is but one of the many ways by which moisture can be added to the unit, and is shown by way of example only. If desired, the units may be passed to a region of humid air, such as for example, a steam chamber, at such a rate that they will remain in it sufliciently long to permit the insulators 3 and 10 to absorb the desired quantity of moisture. 'I'his and many other obvious methods may be employed to introduce moisture into the insulators within the teachings of my invention.

After the insulators have absorbed a certain quantity of water, and have tended to expand longitudinally, the various parts of the assembly will be very tightly clamped together. Since the insulator 10 was placed under compression when the expansion member 29 was removed, any slight elongation of it along its longitudinal axis, or slight thickening of the material radially, will cause an appreciable increase in radial pressure between the shell of the unit and the insulator l0. The insulator 3 will likewise absorb moisture and expand so that the pressure by which the unit 10 is held in the shell is greatly increased.

Expansion of the unit 10, while it goes primarily along'the longitudinal axis of thestrip, since that strip was blanked out of the sheet in'such a manner that the greatest expansion will occur along its longitudinal axis, it will nevertheless expand in all directions. This obviously tightens the resistance winding and securely binds it in place on the insulator so that it will not be displaced thereon by the contactor of the rheostat as that contactor is moved over the resistance.

After the insulation has been allowed to absorb a certain amount of water it is necessary that the moisture content of it be maintained substantially constant if the binding pressure between the insulation and the metallic shell is to be maintained constant. To this end I propose to coat the insulation with a nlm of sealing material, such as for example, oil. In Figure l2 I have illustrated dropping drops 33 of oil onto the insulators 3 and 10 from a suitable receptacle 34. Obviously this is merely a diagrammatic illustration and the oil or other sealing material may be applied in any preferred manner. If desired, the entire unit may be immersed in oil; however, this is a less desirable method of applying it since the entire'shell must then be cleaned to remove the excess.

After the resistance unit and insulator have been coated with a sealing material, a suitable metallic washer 40 is placed inside of the resistor 10 and arivet 41 is projected through it and through the opening formed by the two semicircular openings 26 in the resistance unit 10 and through the circular opening 31 in the shell which is in registration therewith. A .suitable terminal 42 is placed over the projecting end of the rivet and that end is then riveted over as at 'in it, it is not relied upon for support of the resistor in the shell. The rheostat is finished by adding a suitable contactor 44 which for example may be of the type shown in my above mentioned copending application, although obviously any preferred type of contactor may be used within the teachings of my invention.

In certain instances it may be desirable to provide a shell which has a very appreciable amount of iiexibility radially, and to this end I may use a shell such as is shown in Figure 14. Thisshell comprises a circular plate 45 having a ilange 46 rising out of its outer edge, and this iiange 46 is provided with a plurality of outwardly projecting corrugations 47 uniformly spaced around it. The iiange may also be provided with a pair of larger corrugations 48 adapted to receive the terminals 2'? of the rheostat; however, the use of such corrugations is not necessary and if desired they may be omitted.

Obviously when a shell of the type shown in Mgure le is used and expanded by the application of pressure radially outward through expansion of a member suchas 29, the corrugations i7 and 48 will tend to flatten out and therebyr increase the length of the inside face of the shell. When the radial pressure is removed these corrugations will tend to assume their original shape, and the perimeter of the inner surface of the shell will be thereby reduced and the shell will therefore exert considerable pressure against the insulator strips disposed within it.

In the foregoing description of my improvedk process I mention the use of two expanding members 20 and 29 the iirst of which is used to expand the lining insulator of the shell into place and the latter to expand the resistance carrying strip into place. In the manufacture of tandem rheostats in which the lining insulators are comparatively thick, the use of two expanders of this-type may be, highly desirable. In the manufacture of single unit rheostats, there is no necessity of having the insulation lining of the shell so thick, and it may be convenient to use but a single expanding member which is applied after the lining and the resistance carrying strip are positioned in place in the shell. I am not therefore to be limited to the precise details described in the example given by Way of illustration.

While I have chosen to show my invention by illustrating its adaptation to the manufacture of rheostats, I have done so by way of example as 1t is obviously capable of being applied wherever it is desired to retain a fibrous member within a cuplike shell under its own pressure. I am therefore to be limited only by the scope of the appended claims.

Having thus complied with the statutes and shown and described a preferred embodiment of my invention, what I consider new and desire to have protected by Letters Patent is pointed f out in the appended claims. f..

What is claimed is: y

l. A rheostat comprising a cup-like metallic shell, a plurality of corrugations projecting radially outward from said shell, an insulating member lining said shell, a resistance strip slightly longer than the inner perimeter of said insulating lining disposed within said shell and being compressed to cause abutment of its ends against its own arch strength by. compression in said shell and corrugations to lock the strip and insulating member in place in the shell, and a contactor plvotally mounted on said shell and engaging said resistance strip.

2. A rheostat comprising a shell consisting of a closed end metallic cylinder whose walls are slightly flexible, an insulation lining in said cylinder, a wire wound resistance strip having a length slightly greater than the perimeter of the surface of the lining against which it is adapted to bear so that when the strip is disposed in said shell with its ends abutting it is compressed against the tension of the shell and locks itself and the insulation in Athe shell, a sealing material on said strip for maintaining its moisture content substantially constant, and a contactor mounted on said shell and engaging said resistance..A

3. A rheostat comprising a shell consisting of a closed end metallic cylinder whose walls are slightly flexible, an insulation lining in said cylinder, a wire wound resistance strip disposed in said shell with its ends abutting, terminals engaging the ends of said resistance and disposed between it and said insulation, the normal length of said strip being slightly more than the Vperimeter of the surface of the lining against which it is adapted to bear so that the strip, 'when compressed against the tension of the shell to cause abutment of its ends, locks itself, said terminals, and the insulation in the shell, a sealing material on said strip for maintaining its moisture content constant, and a contactormounted on said shell and engaging said resistance.

4. A rheostat comprising a shell consisting of a closed end metallic cylinder whose walls are slightly flexible, a fibrous insulation lining in said cylinder, a wire wound resistance strip adapted to be disposed in said shell with its ends abutting, the normal length of said strip being slightly more than the perimeter of the surface of the lining against which it bears so that the strip, when compressed against the tension of the shell, locks itself and the insulation in the shell, a sealing material on' said,l strip for maintaining-lts moisture content constant, and a contactor mounted on said shell and engaging said resistance.

5. A rheostat comprising a shell consisting of a closed end metallic cylinder whose walls are slightly exible, an insulation lining in said cylinder, a wire resistance unit wound on a fibrous insulation strip disposed in said shell with its ends abutting, the normal length of said strip being slightly more than the perimeter of the surface of the lining against which it bears so that the strip, when compressed against the tension ofthe shell, locks itself and the insulation in the shell, a sealing material on said strip for maintaining its moisture content substantially constant, and a contactor mounted on said shell and engaging said resistance.

6. A rheostat'oomprising a shell consisting of a closed end metallic cylinder whose walls are slightly flexible, an insulation lining in said cylinder, a wire resistance unit wound on a fibrous insulation strip disposed in said shell with its ends abutting, the normal length of said strip being slightly more than the perimeter of the surface of the lining against` which it bears so that the strip, when compressed against the tension of the shell, locks itself andthe insulation in the shell, a film of oil covering said strip to maintain its moisture content substantially constant, and a contactor mounted on'said shell and engaging said resistance.

NEWTON C. SCHELLENGER. 

